Recently, a driving assist system for improving safety, convenience and comfort of a vehicle for a passenger is disclosed in, for example, JP-A-2006-231963. A technique for detecting a face orientation and/or a direction of an eye is used for the system in the vehicle. The face orientation and the direction of the eye are detected based on a data of an image of a face of a human, which is shot by a device. Specifically, with using the face orientation and the direction of the eye, the system determines whether a driver takes his eye off a road. Further, the system estimates physiological state and psychological state of the driver based on variation of feature positions in his face. Thus, the safety, convenience and comfort for the passenger is improved with using information about the inattentive driving, the physiological state and psychological state of the driver.
Further, a shooting method for shooting a face of a human when near infrared light is irradiated on the face of the human and for shooting the face of the human when the near infrared light is not irradiated on the face is described in, for example, JP-A-2007-4448. In this case, a difference image between a shot image when the near infrared light is irradiated on the face and a shot image when the near infrared light is not irradiated on the face is obtained. With using the difference image, the shot image is obtained with reducing influence of an external light such as sunshine.
However, when the near infrared light is irradiated on face of a person wearing glasses, the near infrared light is reflected on a lens of the glasses and/or a frame of the glasses. Thus, a portion with high brightness appears on the shot image.
To remove the high brightness portion on the image, various methods are proposed. For example, a brightness histogram of picture cells, which provide the shot image, is formed, so that some of picture cells having brightness equal to or larger than a predetermined threshold are specified as a high brightness portion. Then, the brightness in the high brightness portion is replaced with average brightness of periphery picture cells around the high brightness portion so that actual brightness of the high brightness portion is reproduced. This technique is disclosed in, for example, JP-A-2002-269545. Further, another technique is disclosed in JP-A-H08-185503. This technique is such that a first threshold for extracting a reflection image of an eye ball of a human is defined, and a second threshold for extracting a reflection image of glasses worn by the human is defined. Then, based on a shape of a binarized image of a shot image processed with using the first and second thresholds, the reflection image from the glasses is removed.
However, when the techniques in JP-A-2002-269545 and JP-A-H08-185503 are used, and the first and second thresholds are set to be certain values, a picture cell not related to the reflection of the near infrared light may be detected, or the high brightness portion provided by reflection of the near infrared light may not be detected. Thus, from a practical standpoint, reliability of detection of the high brightness portion is reduced.
Further, in the technique in JP-A-2002-269545, the brightness of the high brightness portion is replaced with the average brightness of the periphery picture cells. Accordingly, the replaced picture cells may provide a blurry image, and/or the brightness of the image may be uneven. Thus, the reproducibility of the brightness of the high brightness portion is low.